"
"You were wrong, Willis; he likewise told us that sound travels at the
rate of four hundred yards in a second."
"Well, but--"
"Have patience, Willis! When the lightning flashes, the electric spark
is discharged, is it not?"
"Well, I was never high enough aloft to see."
"But others have been; Newton and Franklin have seen it. Now, if the
sound reaches our ears a second after the flash, it has travelled four
hundred yards. If we hear it twelve or thirteen seconds after, it has
travelled twelve or thirteen times four hundred yards, or about half a
mile, and so on."
"But what has that to do with your pulse?"
"In the first place, I am in perfect health, am I not?"
"I hope so, Master Jack."
"Then when our systems are in good order, the pulse, keeping fractions
out of view, beats once in every second; and consequently, though we
do not always carry a watch, we always have our arteries about us, and
may therefore always reckon time."
"Now I understand."
"Ah! then we are to escape this time without the 'Mariner's March.'"
"It appears, Master Jack, that you have turned philosopher as well as
your brothers. Can you tell me what causes lightning?"
"Yes, I can, Willis. You must know, in the first place, that all the
layers of the atmosphere are, more or less, charged with electricity.
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